*I translate a Japanese article into English

A black maestro who is excited about going to GW to eat spicy gourmet food.
This time I tried to summarize the image resolution, the resolution is important for printed matter and the web! 
I would be happy if it would be a hint.
In addition, we will introduce a little trick of Photoshop.

What is image resolution (dpi)?

Resolution is the density of an image, the number of pixels per inch (2.54 cm).
dots per inch is abbreviated as dpi .
In the case of 72 dpi, 72 pixels x 72 pixels per inch = 5184 pixels.
Actually, the image is a large dot picture composed of pixels. 
The higher the resolution, the more pixels per inch = the higher the density and the higher the image reproduction rate.

If you enlarge the red circle,
It’s a dot!

Recommended image resolution for printing / web

Printing: 300dpi ~ * Recommended image resolution varies for printed materials
web: 72dpi

Reasons for printing from 300 dpi

Printing presses have a unit called the number of screen lines , which represents the density at which ink is spread . Naturally, the larger the screen line number, the higher the print reproduction rate.

The number of screen lines varies depending on the printing press, and some high-definition printing presses typically have 150 lines and 300 lines.
The recommended resolution is 150 lines x 2 = 300 dpi because the resolution of the printing press is about 2 x screen lines .

Even if the resolution exceeds the recommended level, there will be no change in the finish due to the limitations of the printing machine. However, if the resolution is below the recommended level, the image may not be printed as expected, such as blurry images.

The difference in handling of the screen line number of the printing machine varies depending on the paper quality and application. 
For example, if printing on a thin paper such as a newspaper with a high screen line number, the amount of ink will be too large and the paper will be distorted and the line will be distorted. Will be printed.
The recommended resolution is 80 lines x 2 = 160 dpi. 

The following is an image of the number of printed lines.

It’s easy to understand if you compare the photos of your newspaper and fashion magazine.

Why web is 72dpi

Because it depends on the resolution of the display, the image resolution is meaningless. No matter how high the resolution image is prepared, it will be displayed depending on the display, so there is no change, so it is enough to consider only the number of pixels (size) of the image. Oh, in fact, the number 72 dpi is just an exception, so it can be 96, 100 or 50.
By the way, this rule is called absolute resolution and is used to indicate the size of images and displays.

72 dpi and 350 dpi images were prepared for confirmation.

72dpi
350dpi

Since it is displayed depending on the resolution of the display, there should be no difference.
In addition, there is a CSS pixel as a way to avoid changing the image size depending on the display resolution on the web .

What is the pixel count of the camera?

By the way , if you explain roughly about “ 50 million pixels! ” In the ugly words of the camera, you can shoot 50 million pixels .
The larger the number of pixels, the higher the amount of expression, so no matter how large the image will be, it will not be doted.

If you tell us that the 1920 x 1080 display has about 2.70 million pixels , can you see the size of 50 million pixels?
When viewing a picture taken with 50 million pixels on a PC, naturally it will not fit in the display, so the picture will be reduced and displayed, but since there is the above-mentioned display-dependent absolute resolution, the difference in the number of pixels is not known It’s crazy.

The strength of the number of pixels is especially true when printing in large sizes such as high-definition printing .
In addition, there are 800 million pixels in the camera that shoots the universe, so you can check everywhere in the universe because you can save the details clearly.
By the way, be careful because the camera doesn’t have to have many pixels!

50 million pixels img
Cannot be displayed on the display

Change image resolution without changing the size  in Photoshop

I want to change the resolution without changing the size! One trick that is useful in such a case.
The resolution can be changed from Image → Image resolution .

Let’s change 350dpi to 72dpi immediately.

!?

Oh, it’s so small! Wow ah ah ah!
Don’t panic … uncheck “Resample”. Only the image resolution can be changed while maintaining the original size.

The size does not change!

Finally

Next, let’s print web images neatly! Kana, after all … But I haven’t tried enough to write an article myself, but I’m curious about how much resolution can be played, so I’d like to find out.

It’s refreshing to be able to put together information that has been postponed within me! 
It seems to have a good holiday! Hot spicy noodle fire!

作者情報
A designer wearing black clothes that has recently started studying the front end and the web. My hobbies are watching horror works and listening to ghost stories. I like very spicy gourmet food.
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